JP4045671B2 - Direct injection spark ignition internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a direct injection spark ignition internal combustion engine in which fuel is directly injected into a cylinder by a fuel injection valve and ignited by a spark plug.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a direct injection type spark ignition type internal combustion engine in which a fuel injection valve has an injection hole facing a cylinder and injects fuel directly into the cylinder by the fuel injection valve is known (for example, (See JP-A-8-144762, JP-A-8-177499, etc.). Many direct injection spark ignition internal combustion engines of this type are provided with a dish-shaped bowl on the piston crown in order to realize stratification of the air-fuel mixture.
[0003]
According to this direct injection type spark ignition internal combustion engine, when the internal combustion engine is at low and medium loads, the fuel-air mixture is injected by injecting fuel toward the bowl formed on the piston crown surface mainly during the compression stroke. It can be formed by stratification, and super lean combustion is possible.
Therefore, the fuel consumption rate at low and medium loads can be reduced. Further, when the engine is under a high load, fuel is injected mainly during the intake stroke, so that there is an advantage that a homogeneous air-fuel mixture can be formed and a high torque can be secured.
[0004]
[Problems to be solved by the invention]
However, in the direct-injection spark-ignition internal combustion engine, especially during stratified combustion, the injected fuel does not reach the piston crown due to the difference between the shape of the bowl formed on the piston crown and the outer shape of the fuel spray. There is a risk that the fuel reaches the uniform surface and increases the amount of fuel adhering to the crown surface of the piston. In addition, the amount of fuel spilling from the bowl may increase, resulting in a decrease in fuel efficiency and combustion stability, and an increase in smoke and HC emissions.
[0005]
[Means for Solving the Problems]
Therefore, the present invention has a dish-shaped bowl having a substantially circular opening on the piston crown and a fuel injection valve that directly injects fuel into the cylinder. In a direct injection spark ignition internal combustion engine that realizes stratified combustion by injecting fuel toward the cross section, the cross-sectional shape perpendicular to the spray direction of the fuel spray by the fuel injection valve is set to the ratio of the opening diameter and the depth of the bowl A flat shape having a corresponding flat rate is set.
[0006]
With the above configuration, the outer shape of the fuel spray becomes an appropriate shape according to the shape of the bowl, and the fuel spray fits in the bowl without excess or deficiency. That is, the fuel spray during stratified combustion is well diffused into the bowl without spilling from the bowl.
Therefore, it is possible to reduce both the amount of fuel adhering to the piston crown and the amount of fuel spilling from the bowl, especially during stratified combustion. As a result, fuel efficiency and combustion stability are improved, and smoke and HC emissions are reduced. The amount can be reduced.
[0007]
Further, the first aspect is characterized in that the flatness is corrected in accordance with the mounting angle of the fuel injection valve.
[0008]
In this case, the outer shape of the fuel spray can be more appropriately matched to the bowl shape according to the mounting angle of the fuel injection valve.
[0009]
In the second aspect , the spray center line of the fuel spray is directed to the corner of the bowl at the piston position at a predetermined fuel injection timing under medium and medium load conditions in the operation region where stratified combustion is performed. The flatness is corrected in accordance with the angle formed by the spray center line and the cylinder reference horizontal plane.
[0010]
That is, the flatness ratio is corrected corresponding to the central portion of the stratified operation region. As a result, the above operations and effects can be appropriately obtained in a wide operating range from a low load to a high load range and from a low rotation to a high rotation range.
[0011]
The present invention is characterized by having a flatness ratio adjusting means for adjusting the flatness ratio in accordance with the operating state of the internal combustion engine.
[0012]
More specifically, as in the third aspect , the fuel spray injected from the plurality of injection holes provided in the fuel injection valve is configured to have a flat shape as a whole, and the flatness ratio adjusting means Is configured to adjust the flatness ratio by changing the fuel pressure to be injected.
[0013]
The flatness is adjusted, for example , according to at least the engine speed.
[0014]
Specifically, since the piston speed is fast at high revolutions, supplying the same amount of fuel into the cylinder as at low revolutions increases the piston travel distance from the start of injection to the end of injection, The amount of fuel adhering to the crown surface will increase. Therefore, it may be possible to suppress the increase in the amount of fuel adhering to the piston crown by increasing the injection timing as the rotational speed increases. However, this may increase the amount of fuel spilled from the bowl. is there. According to the present invention, by increasing the fuel spray flatness as the engine speed increases, the amount of fuel spilled from the bowl can be suppressed without increasing the amount of fuel adhering to the piston crown. Good combustion can be realized.
[0015]
Preferably , the aspect ratio is reduced during idling.
[0016]
That is, during idling, the in-cylinder gas flow is weak, the amount of injected fuel is small, and the piston speed is slow, so that, for example, the injection timing is retarded in order to satisfactorily place the injected fuel in the bowl. For this reason, the time from injection to ignition is relatively short, and if the fuel spray flatness is high to some extent, the fuel concentration increases, so the fuel vaporization time cannot be sufficiently secured, There is a risk of increasing the amount of HC emission. According to the present invention, by reducing the flatness ratio during idling, the fuel spray can be distributed widely to some extent to ensure the fuel vaporization time, thereby suppressing the amount of HC emission.
[0017]
The present invention is characterized in that the flatness is adjusted according to at least the load of the internal combustion engine.
[0018]
For example, at the time of high load in the operation region where stratified combustion is performed, the amount of injected fuel required for one injection increases, so the time from the start of injection to the end of injection becomes longer, and the amount of piston movement during that time is also growing. For this reason, if fuel injection is performed at the same injection (start) timing as during low and medium loads, the amount of fuel adhering to the piston crown increases, so the fuel adhering amount can be increased by increasing the injection start timing. It is conceivable to suppress the increase of. However, if the injection timing is advanced in this manner, the amount of fuel spilled from the bowl may increase. According to the present invention, by increasing the flatness ratio as the engine load increases, the amount of fuel spilled from the bowl can be suppressed without increasing the amount of fuel adhering to the piston crown surface. .
[0019]
On the other hand, at the time of low load, since the amount of injected fuel required for one injection is small, for example, the injection (start) timing is relatively retarded in order to satisfactorily place the injected fuel in the bowl. For this reason, the time from injection to ignition becomes relatively short, and if the fuel spray flatness is high to some extent, the concentration of fuel increases, and as a result, sufficient fuel vaporization time cannot be secured. There is a risk of increasing the HC emission amount. According to the present invention, by reducing the flatness ratio as the engine load decreases, fuel spray can be widely distributed to ensure fuel vaporization time, and the amount of HC emissions can be suppressed.
[0020]
【The invention's effect】
According to the present invention, the outer shape of the fuel spray becomes an appropriate shape according to the shape of the bowl, and the fuel spilled from the bowl is reduced without causing an increase in the amount of fuel adhering to the piston crown especially during stratified combustion. As a result, fuel efficiency and combustion stability can be improved, and smoke and HC emissions can be reduced.
[0021]
Moreover, according to the 1st aspect , according to the attachment angle of a fuel injection valve, the outer shape of fuel spray can be made still more suitable according to the shape of the bowl.
[0022]
According to the second aspect , the flattening rate is corrected corresponding to the central portion of the stratified operation region, and the above-described action is achieved in a wide operation region ranging from a low load to a high load region and from a low rotation to a high rotation region. , The effect can be obtained effectively.
[0023]
According to the present invention, it is possible to adjust the flatness ratio to the optimum according to the operating state of the internal combustion engine.
[0024]
Accordance agencies rotational speed increases, by increasing the aspect ratio of the fuel spray, without increasing the amount of fuel adhered to the crown surface of the piston, it is possible to suppress spill from the fuel bowl, and thus good combustion realizable.
[0025]
During idle by reducing the aspect ratio, the fuel spray by somewhat widely distributed to ensure fuel evaporation time, it is possible to suppress the advance HC emissions.
[0026]
By loading the agencies to increase the aspect ratio according to increase, without increasing the fuel adhered to the crown surface of the piston, it is possible to reduce the fuel spill from the bowl, it is possible to realize a good combustion. Further, by reducing the flatness ratio as the engine load decreases, fuel spray can be widely distributed to ensure fuel vaporization time, and the amount of HC emission can be suppressed.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0028]
FIG. 1 shows a mechanical configuration of a direct injection spark ignition internal combustion engine to which the present invention is applied. This internal combustion engine is mainly composed of a cylinder head 11 and a cylinder block 12, and the cylinder block. A plurality of cylinders 13 are formed in the cylinder 12. A piston 14 is slidably fitted to the cylinder 13, and a recess serving as a part of a combustion chamber is formed on the lower surface of the cylinder head 11 covering the cylinder 13. A port 15 and a pair of exhaust ports 16 are connected, and an intake valve 17 and an exhaust valve 18 are opened and closed respectively. An ignition plug 19 is disposed at the center of the four intake valves 17 and the exhaust valve 18, that is, at the center position of the cylinder 13.
[0029]
An electromagnetic fuel injection valve 20 that opens and closes by an injection pulse signal is disposed directly on the cylinder 13 on the outer peripheral portion of the upper end of the cylinder 13 on the intake valve 17 side. The fuel injection valve 20 injects fuel from a nozzle hole at the tip, and is attached in a posture inclined obliquely downward as shown in the figure.
[0030]
On the crown surface of the piston 14, a dish-shaped bowl 21 having an opening 21a having a substantially circular shape is recessed. The bowl 21 constitutes a part of the combustion chamber, and is partially formed in a range deviated to one of the crown surfaces of the piston 14, specifically, a range deviated to the fuel injection valve 20 side. Is formed so as to include the center of the piston 14 from the vicinity of the outer periphery thereof.
[0031]
The control device 22 for controlling the fuel injection valve 20 and the spark plug 19 is composed of a CPU, ROM, RAM, I / O, etc. as a so-called microcomputer system. The control device 22 includes an engine such as an air flow meter 23 for detecting the intake air amount of the internal combustion engine, a crank angle sensor 24 for detecting the engine speed and the engine crank angle position, and a throttle opening sensor 25 for detecting the throttle opening degree. A detection signal from sensors for detecting the driving state is input. The control device 22 drives and controls the fuel injection valve 20 based on the detected engine operating state.
[0032]
With the above-described configuration, stratified combustion is performed in which fuel is injected toward the bowl 21 during the compression stroke, mainly during low and medium loads of the engine, and combustion proceeds in the bowl 21. On the other hand, mainly at the time of high engine load, fuel is injected into the cylinder 13 during the intake stroke, and homogeneous combustion is performed in which a homogeneous air-fuel mixture is formed in the cylinder 13.
[0033]
2 and 3 show a first embodiment of the present invention. In this embodiment, the outer shape of the fuel spray F injected from the fuel injection valve 20, in other words, the cross-sectional shape perpendicular to the spray direction of the fuel spray F, the ratio Rb / Db between the opening diameter Rb and the depth Db of the bowl 21 is used. Is set to a flat shape (elliptical shape) having a flat rate corresponding to the above. More specifically, the flatness ratio is represented by a ratio L1 / L2 between the major axis L1 and the minor axis L2 in the fuel spray F, and this ratio L1 / L2 is represented by the following equation (1): Rb It is set to be approximately equal to / Db.
[0034]
[Expression 1]
L1 / L2≈Rb / Db (1)
As a result, the outer shape of the fuel spray F becomes an appropriate shape according to the shape of the bowl 21, and the fuel spray F fits in the bowl 21 without excess or deficiency. That is, the fuel spray F at the time of stratified combustion is favorably diffused into the bowl 21 without spilling from the bowl 21. Accordingly, it is possible to reduce the amount of fuel adhering to the crown surface of the piston 14 and the amount of fuel spilled from the bowl 21 particularly during stratified combustion, and as a result, improve fuel efficiency, combustion stability, smoke and HC emissions. Can be reduced.
[0035]
FIG. 4 shows a second embodiment of the present invention. In this embodiment, the flatness L1 / L2 is corrected according to the mounting angle α of the fuel injection valve 20. The attachment angle α is represented by an angle formed by the center axis Q of the fuel injection valve 20 that coincides with the spray center line P1 of the fuel spray F and a cylinder (cylinder head) reference horizontal plane. That is, the flatness L1 / L2 is expressed by the following equation (2).
[0036]
[Expression 2]
L1 / L2≈Rb / Db · sin α (2)
As a result, the height (L2 · cosα) of the fuel spray F in the cylinder axial direction is appropriate according to the depth Db of the bowl 21. Therefore, even in an internal combustion engine in which the mounting angle α of the fuel injection valve 20 and the shape of the piston 14 are different, the outer shape of the fuel spray F can be made appropriate according to the shape of the bowl 21, and the first embodiment described above. The same actions and effects as the example can be extracted optimally.
[0037]
FIG. 5 shows a third embodiment of the present invention. In this embodiment, the spray center line P2 of the fuel spray F is a corner portion of the bowl 21 at the position of the piston 14 at a medium speed and medium load condition in an operation region where stratified combustion is performed and at a predetermined fuel injection timing. 21b, more specifically, is set so as to face the corner 21b between the bottom and the side wall of the bowl 21. The flatness L1 / L2 is corrected according to the angle β formed by the spray center line P2 and the cylinder reference horizontal plane. More specifically, the flatness ratio L1 / L2 is expressed by the following equation (3).
[0038]
[Equation 3]
L1 / L2≈Rb / Db · sinβ (3)
In this embodiment, the spray center line P2 of the fuel spray F is deflected by (α−β) with respect to the center axis Q of the fuel injection valve 20.
[0039]
According to this embodiment, the flatness is corrected corresponding to the central portion of the stratified operation region, and in the wide operation region from the low load to the high load region and from the low rotation to the high rotation region, The same operations and effects as those of the second embodiment can be obtained appropriately.
[0040]
FIG. 6 shows a fourth embodiment of the present invention, and the structure of this embodiment is applied to, for example, the first to third embodiments. In this embodiment, two injection holes 30 are provided along the major axis direction of the fuel spray F (Fa or Fb) at the tip of the fuel injection valve 20, and the fuel spray Fa (or the fuel spray Fa (or fuel injection) injected from each injection hole 30 (or Fb) is combined to form a flat shape as a whole. That is, the distance S between the injection holes 30 and the injection angle θa (or θb) are appropriately set so as to obtain the desired flatness ratio L1 / L2.
[0041]
Here, the injection angle θa (θb) of the fuel spray Fa (Fb) injected from each injection hole 30 changes according to the pressure (fuel pressure) of the injected fuel. FIG. 6A shows a case where the fuel pressure is relatively low, and FIG. 6B shows a case where the fuel pressure is relatively high. As shown in FIG. 6A, when the fuel pressure is relatively low, the injection angle θa of each fuel spray Fa becomes relatively large. As a result, the overall flatness ratio L1 of the two fuel sprays Fa combined. / L2 becomes relatively small. On the other hand, as shown in FIG. 6B, when the fuel pressure is relatively high, the injection angle θb of each fuel spray Fb becomes relatively small, and as a result, the overall flatness of the two fuel sprays Fb combined. The rate L1 / L2 is relatively large. That is, as the fuel pressure increases, the flatness L1 / L2 increases.
[0042]
Therefore, the flatness L1 / L2 of the fuel spray F can be appropriately adjusted by variably controlling the fuel pressure with the control device 22 in accordance with the operating state of the internal combustion engine.
[0043]
For example, the flatness ratio L1 / L2 is adjusted according to the engine speed detected by the crank angle sensor 24. That is, since the piston speed is fast at the time of high rotation, if the same amount of fuel is supplied into the cylinder 13 as at the time of low rotation, the moving distance of the piston 14 from the start of injection to the end of injection becomes large. The amount of fuel adhering to the crown surface will increase. Therefore, it is conceivable to suppress an increase in the amount of fuel adhering to the crown surface of the piston 14 by increasing the injection (start) timing as the rotational speed increases. In this case, however, the amount of fuel spilled from the bowl 21 May increase. According to this embodiment, as the engine speed increases, as shown in FIG. 6 (b), the fuel spray amount on the crown surface of the piston 14 is increased by increasing the flatness L1 / L2 of the fuel spray Fb. Without increasing the amount of fuel, the amount of fuel spilled from the bowl 21 can be suppressed, and good combustion can be realized.
[0044]
Further, the flatness ratio L1 / L2 is reduced during idling. That is, during idling, the gas flow in the cylinder is weak, the amount of injected fuel is small, and the piston speed is slow. In order to satisfactorily place the fuel spray in the bowl 21, for example, the injection (start) timing is set. Need to retard. For this reason, the time from injection to ignition becomes relatively short, and if the fuel spray flatness L1 / L2 is high to some extent, the fuel concentration increases, so that sufficient fuel vaporization time is secured. This cannot be done, and there is a risk of increasing the amount of HC emission. According to the present embodiment, by reducing the flatness ratio L1 / L2 during idling, the fuel spray Fa is distributed to a certain extent as shown in FIG. Can be suppressed.
[0045]
More preferably, the flatness L1 / L2 is adjusted according to the load of the internal combustion engine. That is, at the time of high load, the amount of injected fuel required for one injection increases, so the time from the start of injection to the end of injection becomes longer, and the amount of movement of the piston 14 during that time also increases. For this reason, if fuel injection is performed at the same injection timing as when the load is low, the amount of fuel adhering to the crown surface of the piston 14 will increase. It is possible to make it. However, if the injection timing is advanced in this way, the amount of fuel spilled from the bowl 21 may increase. According to the present embodiment, the amount of fuel spilled from the bowl 21 without increasing the amount of fuel adhering to the crown surface of the piston 14 by increasing the flatness ratio L1 / L2 as the engine load increases. Can be suppressed, and good combustion can be realized.
[0046]
On the other hand, at the time of low load, since the amount of injected fuel required for one injection is small, the injection timing is relatively retarded, for example, in order to satisfactorily store the injected fuel in the bowl 21. For this reason, the time from injection to ignition is relatively shortened, and when the fuel spray flatness L1 / L2 is high to some extent, the fuel concentration increases, and as a result, the fuel vaporization time is sufficient. This cannot be ensured, and there is a risk of causing an increase in HC emissions. According to the present embodiment, the flattening rate L1 / L2 is lowered as the engine load is reduced, so that the fuel spray Fa is widely distributed as shown in FIG. The amount of HC emission can be suppressed.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration of a direct injection spark ignition internal combustion engine according to the present invention.
FIG. 2 is a configuration diagram showing a first embodiment of the present invention.
FIG. 3 is a cross-sectional view corresponding to the AA cross section of FIG. 2 showing the first embodiment.
FIG. 4 is a configuration diagram showing a second embodiment of the present invention.
FIG. 5 is a configuration diagram showing a third embodiment of the present invention.
FIG. 6 is an explanatory view showing a fourth embodiment of the present invention.
[Explanation of symbols]
13 ... Cylinder 14 ... Piston 20 ... Fuel injection valve 21 ... Bowl F ... Fuel spray

Claims (6)

A dish-shaped bowl having a substantially circular opening is recessed in the crown of the piston, and has a fuel injection valve that directly injects fuel into the cylinder, and injects fuel toward the bowl near the compression stroke. In a direct injection spark ignition internal combustion engine that realizes stratified combustion,
The cross-sectional shape perpendicular to the spray direction of fuel spray by the fuel injection valve is set to a flat shape having a flatness ratio according to the ratio of the opening diameter and depth of the bowl,
And it has a flatness ratio adjusting means for adjusting the flatness ratio according to the operating state of the internal combustion engine,
This flat rate adjusting means increases the flat rate as the engine load increases in the operating region where the stratified combustion is performed .   2. The direct injection spark ignition internal combustion engine according to claim 1, wherein the flatness adjusting means increases the flattening rate as the engine speed increases. 3. The direct injection spark ignition type internal combustion engine according to claim 1, wherein the flatness ratio adjusting means reduces the flatness ratio during idling. The direct-injection spark ignition internal combustion engine according to any one of claims 1 to 3 , wherein the flatness ratio is corrected in accordance with a mounting angle of the fuel injection valve. The fuel spray center line is set so as to be directed to the corner of the bowl at the piston position at a predetermined fuel injection timing under medium and medium load conditions in the operation region where stratified combustion is performed. And
The direct-injection spark ignition internal combustion engine according to any one of claims 1 to 3 , wherein the flatness ratio is corrected in accordance with an angle formed by the spray center line and a cylinder reference horizontal plane. The fuel spray injected from the plurality of injection holes provided in the fuel injection valve is configured to have a flat shape as a whole,
The aspect ratio adjusting unit, a direct injection spark ignition type internal combustion engine according to any one of claims 1 to 5, characterized in that adjusting the aspect ratio by changing the fuel pressure to be injected.

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